As someone noted earlier, specialization is key to efficiently using multiple machines. Among other things, I have an imac, macbook pro, and ipad that I use together for a combination of work and leisure, and work includes science research, music composition and recording, and some graphic design and website creation. Leisure = music, movies, and some gaming. I "sync" these devices using dropbox, evernote, and some external hard drives.
Here's what I use, and for what:
1) iMac - This is my powerhouse and testbed. I install everything on this machine, and I use it as a media centre and a work computer, and I do some gaming on it as well. From photoshop to starcraft 2, I throw everything at this machine. In that respect, it's pretty straightforward. I also use this machine for iTunes (with my ipad and ipod).
2) Macbook Pro - I use this for mobile "work" (e.g. Microsoft Office, Photoshop, etc.), but it's primarily for music production, so I run Ableton, Logic, and Garageband on it... along with some other stuff... Because it's my main music production machine, I try to keep this laptop very clean and efficient in terms of software. I install a minimum of unnecessary software (e.g. games) so that it runs fast and smooth and efficiently.
3) iPad - I use this mostly for leisure, but I do some work on it. This is my convenient and fun mobile computer. I use it around the house and for travelling, for all my day to day stuff (web browsing, email, etc.). That being said, I do use Pages on it for document creation, and apps like evernote for writing and getting down ideas, etc.
So, those are my main devices, along with their divisions of labour.
I tie these together using external hard drives (for big files and back ups), but I use dropbox and evernote to really sync them.
Dropbox is used for various types of files (e.g. word documents, that sort of thing), and I use Evernote for text-based information (everything from to-do lists to ideas or written content that I will later turn into a nice document, etc.).
Dropbox and Evernote are the glue that ties my devices together, I suppose, and as you can see my different devices serve different purposes, although there is some overlap in this.
Hope that helps!
